In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization. Typically, these pattern miniaturization techniques involve shortening the wavelength (and increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in the mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a shorter wavelength (and a higher energy level) than these excimer lasers, such as electron beam (EB), extreme ultraviolet radiation (EUV), and X-ray.
As the wavelength of exposure light sources is shortened, the resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. A known type of resist material that satisfies these conditions is a chemically amplified resist composition.
For example, in the case where the developing solution is an alkali developing solution (namely, an alkali developing process), a chemically amplified resist composition containing a resin component (base resin) which exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator is typically used. If the resist film formed using the chemically amplified resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, acid is generated from the acid generator component, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution. The unexposed portions remain as a pattern, resulting in the formation of a positive-type pattern.
The aforementioned base resin uses a resin for which the polarity increases under the action of acid, resulting in an increase in the solubility of the resin in an alkali developing solution, but a decrease in the solubility of the resin within organic solvents. Accordingly, if a process that uses a developing solution containing an organic solvent (an organic developing solution) is employed (hereinafter also referred to as a solvent developing process or negative-type developing process) instead of the alkali developing process, then within the exposed portions of the resist film, the solubility in the organic developing solution decreases relatively, meaning the unexposed portions are dissolved in the organic developing solution and removed, whereas the exposed portions remain as a pattern, resulting in the formation of a negative-type pattern. Patent Document 1 proposes a negative-type developing process.
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as base resins for chemically amplified resist compositions that use ArF excimer laser lithography or the like, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 2).
Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.
Further, besides the base resin and the acid generator, conventional chemically amplified resists also frequently include a nitrogen-containing organic compound such as an alkylamine or alkyl alcohol amine (for example, see Patent Documents 3 and 4). These nitrogen-containing organic compounds act as quenchers that trap the acid generated by the acid generator, thereby contributing to an improvement in the lithography properties such as the resist pattern shape.